Manufacture of zinc oxide



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May 59 1928.

J. A. SINGMASTER ET AL MANUFACTURE oF zINc oxIDEv vFiled March 27, 192e @m6 6 Z #d 2 Sg um 4 Ecc 2 3 MM 4 in Patented Ma'y l5, 19278.'

l A1,670,169 A UNITED s'rn'resI PATENT or'siic'ziiz.-

JAMES A. SINGHASTER, I' BRONXVILLE, NEW YORK, FRANK G. IBREYER A .I'Dv

PENNSYLVANIA, ASSIGNOBS T0 THE .NEW

EARL H. BUNCE, 0F PALHERTON,

JERSEY ,ZINC COMPANY, 0F NEW YORK, N. Y., A COBPOBATIGN OF NEW JERSEYv l i MANUEACTURE 0F ZINC'OXIDE.

Applicationl tiled March 27,19%. Bei-tal Eo.. 97,855.

` This invention relates to the manufacture of zinc Aoxide and has for its object the provision of certain improvements in zinc oxide manufacture. More particularly, the invention aims to provide an improved process of making rubber reinforcing zinc oxide. Other objectsof the invention will be brought 'out a in the course of the following description.

' of this patent depend to some extentv United States Patent No. `1,t' 22,097 BreyerGaskil1 and Singmaster) dated anuary' 6, 1925, describes an improved method of manufacturin zinc oxide in which a blast of relativey cool oxidizing gas isv directed,` against an issuing stream of metallic zinc va or. We have discovered that the physical pro erties of the zinc oxide product produced y the method upon the source of the issuing stream of zinc va or, thatis to say, the method used the zinc vapor. When the -inl pro ucin g the volatilizazinc vapor is produced b tion of `hi h grade metallic zinc, theizincoxide pro uct resulting from the process of this patent is free, or substantiall free, from` impurities9 such as chlorides, su

fates, etc. We have discovered, however, that when the zinc vapor is obtained from a charge of mixed zinciferous andcarbonaceous materials, the 'zinc oxide product produced by the method of this patent almost invariably contains impurities which, al though present in very minute quantities, exercise a pronounced deleterious edect on the zinc oxide when incor orated injrubber. As a result oour -researc es and investigations, we believe that minute amounts of sulfur-oxygen compounds and the like, con-v` dense on the surface o the zinc oxide articles when the zinc vapor is obtained rom a charge of mixed zinciferous and carbonaceous materials, and that these com ounds are responsible, in large measure, or the aforementioned deleterious effects.

The present invention is based upon our discover)7 that the condensation of sulfuroxyen compounds upon the surface of zinc oxi e particles is very substantiallyr inhibited when the se eration of the zinc oxide articles from tlie gases in which these particles are suspended is carried out at temperatures in excess of about 125 '0. Thus, we have ``found that when'the gases carrying the zinc are passed oxide particles in suspension through an appropriate zinc oxide collect- :ing apparatus maintained at a temperature not less than v125 C., the sulfur-oxygen com. pounds (for the most" part sulfur dioxide and sulfur trioxide ."pass along with the exhaust gases and su stantially little, if any.,

objectionable condensation of these-coms.

pounds takes place on the surface ot the zinc'l rials supported on a perforated grate and throu h which a combustion supporting ldraft is passed. The resulting gaseous products containing metallic zinc vapor are oon- .veyed to an oxidizing environment of such characteristics that the zinc oxide particles are substantially instantaneously cooled to tem e'rature` not higher than about 700 an in accordance with our present invention, this sudden chilling or cooling of the zinc oxide articles is so regulated and. controlled that t e gases in whchthe zinc oxide particles are suspended are not cooled below a temperature of 125 C. until after passage through the zinc. oxide collecting apparatus. Thus, the gases and zinc oxide particles suspended therein are maintained at a. temps ture below 700 C., but not less than 125 C., and are conveyed to an appropriate zincoxide collecting a '"aratus where the exhaust gases are remove iroin the zinc oxide product at a temperature not less than about f and supported upon a travelling or moving als 'perforatedgratm through which a combustion supporting draft is maintained. This practice is more fully described in our United States Patent No. 1,322,143. The. character and composition of the briquetied charge and the manipulation of the furnace are so controlled and regulated that a substantially complete non-oxidiziiig atmosphere is maintained above the charge. The resulting gaseous products contain metallic zinc vapor' and are passed vthrough appropriate gas outlets in the roof of the furnace and are conveyed into an oxidizing cnvironment where such products are Isubjeeted to the action of a blast of relatively cool oxidizing gas whereby the flame tem- A, perature is lowered and the resulting parlus substantially instannot higher ticles of zinc oxide are taneously cooled to a temperature than about 700 C., and preferably not higher than about 500 C. The gases and zinc oxide particles suspended therein are then conveyed from this oxidizing environment, while maintained at a temperature not less than about 125"A C., to the zinc oxide collecting apparatus, o preferably asbestos fibre bags, also maintained at a temperature not less than about 125 C.

The novel features of the invention can" be best explained by Ireference to the accompanying drawing in which:

Fig. 1 is a sectional .side elevation of a traveling grate furnace and zinc oxide coll lecting apparatus;

Fig. 2 is a to plan 4view of the furnace and apparatus s iown in Fig. 1; and

Fig. 3 is a detail section on the line 3--3 of Fig. 2.

The travelinnr grate furnace 10 is pro-` vided at'one end thereof with a fuel-briquet feed hopper 11. An adjustable fuel-briquet leveler 12 depends from the furnace roof to within a predetermined height from the perforated traveling grate 13. The fuelriquet ignition chamber 14 has a fuel-ore briquet feed hopper 15 immediately adjoining it. A grizzly chute 16 surrounded by a sheet steel casing 17 inclines downwardly into the fuel-ore briquet hopper.

The fuel-briquet ignition chamber 14 is provided with an outlet 18 through the furnace roof, in conjunction with which is at tached an oftake pipe 19 connected with distributing pipes 20 leadin under the grizzly chute 16. An adjustagl quctleveler 21, adjacentthe fuel-ore briquet hopper 15, depends from the furnace roof to within a predetermined height from the perforated traveling grate 13. The main working chamber 22 extends along vthe greater part of the furnace length. It is provided with outlets 23 through the furnace roof. A gas compartment or Windbox 124, having a conical nozzle 25, rests axially over each outlet 23. These windboxes are equipped with air supply pipes 26 as weil as with circumferential slots 27' A feed pipe 32 extends from the fan to the distributing pipes 33. These pipes in turn lead into a zinc oxide collecting chamber or the suction-blast fau 30 operatively connected with a motor 3l.

bag room 34, the walls and roof of which are insulated with asbestos board, or the like. Filter-bags 35, preferably of asbestos fibre, are hung within the chamber 34 and are connected at their upper ends to the distributing pipes 33, and at their lower ends to collecting hoppers 36. The chamber or bag room 34 is mounted on anappropriate foundation 38. Suitable outlets (not shown) are provided in the topof the bag room to permit the escape of exhaustv gases from the filter-bags to the outside atmosphere.

Returning now to the furnace structure, a relativel short chamber 39 is provided, by depending bulkheads 'or partitions 45, beyond the main workingchamber 22. The chamber 39 has an outlet 40 connected with va down-leg pipe 41 leading to a bag room or other suita Shown). y

A still shorter chamber 42 is provided near the discharge end of the traveling and adjacent to the chamber 39. A stack 43 communicates with this chamber 42 and leads to the outside atmosphere.

A spent residue or ash' hopper 44 is provided at the extreme end of the furnace'to catch exhausted charge clinkers remaining after the furnacing operation has been comle collecting apparatus (not the fuel-briquet hopper 11 at one end of the .furnace 10. The grate is made to travel (by machinery not shown, but more fully described in Patent No. 1,322,143, hereinbefore referred to) with its burden of fuel briquets toward the other end of the furnace as a e fuel-ore bricontinuous but regulated ydraft of combustion supporting gas (preferably air) is passed up through the charge. These fuel briquets are thereupon spiead over .the grate to forma layer of predetermined depth by means of the adjustable levelers 12. They ai'e quickly heated to a relatively high tem erature and ignited as they progress througii the ignition chamber 14.

In the meantime fuel-ore briquets are grate 13,'

pleted rIt is so constructed that the ash may the perforated grate int-o passed down the grizzly chute 16 into the fuel-ore briquet hopper 15 which de osits the briquets upon the ignited la'yer o fuel briquets issuing from the ignition chamber 14. These fuel-ore briquets are fed from the briquetting press (not shown) directly to the furnace by way of the heating chamber 17 surrounding the grizzly chute 16. -Regulated amounts of hot gaseous products of combustion are conducted from the ignition chamber 14 by wayo the off-take pipe 19 and the distributing pi es 20 to a suitable outlet beneath the grizz y chute, where they escape and circulate in and among the descending fuel-ore briquets.

The fuel-ore briquets from the hopper 15 are spread to form a layer of predetermined thickness upon the ignited bed of fuel briquets by means of the adjustable leveler 21. Reduction 'of the compounds of zinc in the fuel-ore briquets to metallic zinc begins to take place almost immediately. The metallic zinc is likewise immediately volatilized to zinc vapors. The greater part of the reduction and volatilzation of the zinc takes place as the traveling grate moves through 'the main working chamber 22 of the furnace. The draft of combustion supporting gas passed .up through the perforated grate is so regulated that a substantially complete non-oxidizing atmosphere is at all times maintained above the charge.

As the combined'charge of fuel and fuelore briquets passes through the main working chamber 22 of the furnace, the gaseous products of the operation, including the metallic zinc vapor, flow, to the outlets 23 and upwardly through the nozzles 25 of the Wind boxes 24. A blast of relatively cool oxidizing gas is directed from the circumferentialslots 27 against the stream of geesons products issuing from the nozzles 25.

y This oxidizing gas, preferably air, is fed under pressure to the wind-boxes by means of pipes 26 and 26.

The metallic zinc vapor issuing from the nozzles 25 immediately oxidizes or burns to zinc oxide, and as a consequence of the action of the blast of relatively cool .oxidizing gas, the dame temperature is vlowered and the resulting particles of zinc oxide are substantially instantaneously cooled to a temperature not more than i700" (Land not higher than about 500 C. rihis lowering'of the ame temperature and substantially instantaneous cooling prevents the initially verv fine zinc oxide particles from fusing, subliming or growing into agglomeratea or particles of larger size.

, The temperature to which the resulting particles of zine oxide should be substan tially instantaneously cooled depends, to some extent at least, upon the concentration of the zinc va or in the gaseous products issuing from t e outlets 23 of the furnace.

preferably suspended in the resulting gases of the oxie dizing operation, are drawn into the hood 28 and piping system 29 by the suction fan 30 and conveyed to the bagroom 34. The bagroom is maintained at a temperature not below about 125 C. The zinc oxide` particles are deposited inthe bags 34, while the gases in which these particles were suspended filter through the bags and exhaust from the bag-room throu h appropriate outlets. The zinc oxide is collected in the hoppers 36, to facilitate which the bags ma be mechanically or otherwise shaken, andy the product collecting in the hoppers is removed in any appropriate manner. lf' the zinc oxide product is held in the hop ers 36 for any ength of time, it is desira le to maintain these hoppers and the oxide therein at a temperature'vnot below about 125 C.

The separation of the zinc oxide articles from the gases in which these partlcles are suspendedwhile maintained at a temperature not below about 125 C., edectively minimizes the condensation of sulfur-oxygen compounds on the surface of the zinc oxide particles. The condensation of such sulfur-oxygen compounds on the surfaceof ature there is still some condensation of the sulfur-oxygen compounds, but the amount of such condensation inthe time the zinc oxide is ordinaril held in the collecting system is not sudicient to deposit a harmful amount of the sulfur-oxygen compounds on the zinc oxide particles. When the zinc oxide is caught vin settling chambers and held exposed to the sulfunox gen gases coming from the furnace for a. enger time Vthan in the ordinary bag-room practice, temperatures higher than 125 C. may be necessary to inhibit objectionable ,condensation of the sulfur-oxygen compounds on the particles of zinewoxide.

A lower grade of zinc oxide is produced inthe traveling grate furnace as the fuel and tueleore briquets become Worked o.

Thus, when the ycharge has been carried by thetraveling grate beyond the main worknaccs, and 4with or propriete collecting apparatus where the zinc oxido is separated from thc gases in which it issuspended. f

The Worked-off charge or residue is dc- )osited from the discharge end of the traveling grate into the receiving hopper 44 und the traveling grate returns by way of its underco-urse to the charging end of the furnace where fresh fuel briquets and fuel-ore briquets are being continuously deposited ou the grate.v The furnace is thus ymechanically operated in a continuous manner.

While we have'herein described the practice of our invention on a traveling grate. furnace with a briquctted charge, it is to be understood vthat' the invention may be carried out in various other types of furwithout briquetting of the charge either in whole or in part.

1..'lhe improvement in the process of making zinc oxide where a charge of zincifcrous and carbonaccous materials is lsnpported on a perforated grate and a combustion supporting draft maintained therethrough, which comprises maintaining substantially non-oxidizing conditions above the charge, conducting the resulting gaseous products containing metallic zinc vapor to an oxidizing environment Where such .products are subjected to the action of a blast of relatively 4cool oxidizing gas, and conveying the resulting gases carrying 'the zinc oxide particles in suspension While maintained at a temperature not less than about 125 C. to an appropriate zinc oxide collecting means where the exhaust gases are separated from the zinc oxide particles at a' temperature not less than about 125 C.

2. The improvement in the process of making zinc oxide Where a charge of zincifcrous and carbonaceous materials is sup-V ported on a perforated grate and-a combustion supporting draft maintained therethrough, which comprises maintaining substantially non-oxidizing the cliargecand conveying the resulting gase- I ous products containing metallic zinc vvapor to an oxidizing `environment where such last of relatively cool oxidizing. gas and the resulting particles of zinc oxide are instantaneousl to a temperature not higher than about 00 C.,

'.and separating the zinc -oxide particles from the gases in which these particles are suspended while maintained at 'a temperature not less than about 125 C.

3. The improvement making zinc oxide where a charge of zincifcrous and carbonaceous materials is heated to a temperature sufficiently high to reduce the compounds of zinc and to volatilizc the metallic zinc, which comprises maintaining substantially 4non-oxidizing conditions above the compounds of zinc and conditions above Y roducts are subjected to the action .of ai" in the process otthe charge, conducting the resulting gaseous products containing metallic zinc vapor to an oxidizing environment, and conveying the resulting gases carrying the zinc oxide particles in suspension while maintained at a temperature not less than about 125 C., to an appropriate zinc oxide collecting lneans where the exhaust gases are lseparated from tlieznc oxide particles at a temperature not less than about 125 C.

4. The improvement in the process of y ing particles of zinc oxide to a temperature' not higher than about 700 C., and separatingr the zinc oxide particles from the gases in which these particles are suspended while maintained at a temperatura-not less than about 125 C. c i' 5. The improvement in the process 0f making zinc oxide where a charge of zincif` crous and carbona'ceous materials is heated to a temperature lsutliciently highl to reduce to volatilize the metallic zinc, which comprises maintaining `substantially non-oxidizing conditions above the charge, conducting the resulting gaseous products containing `netallic zinc vapor to an oxidizino environment Where such products are subjected to the action oty a blast of relatively cool oxidizing. gas, and conveying the resulting gases. carryingl the zinc oxide particlesin suspension while maintained at a temperature not less than about 125 C. to an appropriate zinc oxide collecting means. Where the exhaust gases are removed from the zinc oxide particles at a temperature not less than about 125 C.

6. The improvement in the process of making -zinc oxide where a char erous and carbonaceous materia s is heated to a temperature sufficiently high to reduce the compounds of zinc `and to volatilize the metallic zinc, which comprises maintaining substantially non-oxidizing conditions above the charge, conducting the resulting gaseous products containing metallic zinc vapor to an oxidizing environment where such produets are subjected to the action of a. blast of relatively cool loxidizing gas and the resulting articles of zinc oxide are cooled substantia ly instantaneously to a temperature not higher than about 700 C., and separatine the zinc oxide particles from the gases in which these particles are suspended while maintained at a temperature not less than about 125 C.v

7. The improvement in the process of e of zincify neven lmaking zinc oxide from an appropriately heated charge of zinciferous and carbonaceous materials, which comprises conveying the gases in which tlie particles of zinc oxide are suspended while maintained at a teiliperature not loss than about 125 C. to an appropriate zinc oxide collecting means where the exhaust gases are removed from the zinc oxide particles at a temperature not less than about 125 C.

8. 'lhe improvement in the process of making zinc oxide from an appropriately heated charge of zinciferous and carbonaceous materials, which comprises conducting the formation of the zinc oxide particles in an'oxidizing environment where the particles of zinc oxide are cooled to a temperaturenot higher than about 700 C., substantially instantaneously after their formation, and separating the zinc oxide particles from the gases in which these particles are suspended while maintained at a temperature not less than .about 125 C.

9. 'llie improvement in the process of making zinc oxide where a charge of zinciicrous and carbonaeeous materials is heated to a temperature suciently high to reduce the compounds of zinc and to volatilize the metallic zinc, which comprises conducting the resulting gaseous products containing metallic zinc vapor to 'an oxidizingI environment and there subjecting suchproducts to a blast of relatively cool oxidizing gas whereby the dame temperature is lowered and the resulting 1particles of zinc oxide are cooled substantie ly instantaneously to a temperature not higher than about 'i' 00 C., and conveying the resulting gases carrying the zinc oxide particles in suspension while maintained at a temperature not less than about 125 C. to an appropriate zinc oxide collecting meansV and there separating the exhaust gases from the zinc oxide particles at a temperature not less than about 125 C.

10. The improvement in the process of making zinc oxide `where a charge of mixed zinciferous and carbonaceous materials is supported on a perforated grate and a combustion 'supporting draft maintained there.

through, which comprises maintaining sub- Y stantially non-oxidizing conditions above the charge, conducting the resulting gaseousy products containing metallic eine vapor to an oxidizing environment and there subjecting such products to a blast oi relatively cool oxidizing gas whereby the dame tcmperature is lowered and the resulting particles oi aine oxide are cooled substantially instantaneously to a tern erature not higher than about 700 C., an conveying the resulting gases carryin the eine oxide particles in suspension wille maintained at a tempera-ture noi less than about 125 C., te an appropriate zinc oxide collecting means and there separating the exhaust gases from the zinc oxide particles at a less than about 125 C.

11. The improvement in the process of making zinc oxide where a charge in: whole or in part biiquetted of mixed zincifei'ous and carbonaceous materials is supported on a perforated grateand a combustion su porting draft maintained therethrou E, which comprises maintaining substantially non-oxidizinf conditions above the charge, conducting tieresulting gaseous products containing metallic zinc vapor to an oxidizing environment and there subjecting such products to a -blast of relatively cool oxidiztemp'erature not ing gas whereby the flame temperature is lowered and the resulting particles of zinc oxide are cooled substantially instantaneously to a temperature not higher than about 700 C., and conveying the resulting gases carrying the zinc oxide particles in suspension while maintained at a temperature not less than about 125 C. to an appropriate zinc oxide collecting means and there separating the exhaust gases from the aine oxide particles ata temperature not less than 12. The improvement in the process of making zinc oxide Where a charge of mixed zinciferous and carbonaceous materials is advanced through a combustion zone and a combustion supporting gas is simultaneously passed into'the charge, `vvliich comprises maintaining substantially non-oxidiain conditions above the charge, conducting t e resulting gaseous products containing metallic zinc vapor to an oxidizingv environment vvliere such roducts are subjected to the action of a blpast of relatively cool oxidizing gas, and conveyin the resulting gases carrying the zinc oxi e particles in suspension While maintained at a temperature not less than about 125 C. to an appropriate zincv ies the action oi a blast of relatively cool oxidizl ing gas and the resulting articles of zinc oxide are cooled substantiallyinstantaneously to a temperature not higher than about 700 C., and separating the zinc oxide articlee from the gases in which these particles are suspended while maintained at a temperature not lese than about C.

charge, which comp 14. The improvement in the process of making zinc oxide Where a charge in whole or in part briquetted of zinciferous and carbonaceous materials is advanced lthrough a. combustion zone and a combustion supporting gas is simultaneously passed into the rises maintaining substantially nonoxid1zin conditions above the charge, conducting t e resulting gaseous products containing metallic zinc vapor to`v an oxidizing environment where such proda ucts are subjected to the action of a blast of v relatively cool. oxidizing gas, andconveying y the resulting gases carryin the zinc oxide particles in suspension Whi e maintained at a temperature not less than about 125o il to an appropriate zinc oxide collecting means where thel exhaust gases are separated vfrom the zinc oxide particlesat a temperature not less than about 125 C.

15. The improvement in the process of making zinc oxide where a charge in whole or in part briquetted of zinciferous and carbonaceous materials is advanced through a combustion zone and a combustion supporting gas 1s simultaneously passed into the charge, which comprises maintaining substantially non-oxidinglconditions above the charge, conveying t e resulting gaseous products containing metallic zinc vapor to an oxidizing environment and there sub jecting such products to the action of a blast of relatively cool oxidizing gas whereby the resulting articles of zinc oxide are cooled substantial ly instantaneously to a temperature not higher than about 700 C.,and separating the zinc oxide particles from the gases in which these particles are suspended while maintained at a temperature notless `than about 125 C.

16. The improvement inthe method of making zinc oxide by the American process whereby the. deposition of sulfur-oxygen compounds on substantially inhibited which comprises conveying the zinc oxide laden fume While maintained at a temperature not less than about 125 C. to an appropriate zinc oxide collecting means and there separating the exhaust ases containingthe sulfur-oxygen compoun s from the zinc oxide particles at a temperature not less than about 125 C.

17. The improvement in the method'of making zinc oxide by the American procesa whereby condensation of acid gases on the particles of zinc oxide is substantially iniibited 'which comprises conveying the zinc oxide .laden fume while maintained at a temperature not less than about 125 C. to

an appropriate zinc oxide collectin means, and separating the zinc oxide partie es from the ses in which these particles are suspen not less than about 125 C. y

In testimony whereof we affix our signatures.

JAMES A. SINGMASTER. FRANK G. BREYER.' EARL H. BUNCE.

-the zincoxide particles is' edv while maintained at a temperature 

